Multi-Functional Potassium Ion Assists Ammonium Vanadium Oxide Cathode for High-Performance Aqueous Zinc-Ion Batteries

Ammonium vanadium oxide (NH4V4O10) is a promising layered cathode for aqueous zinc-ion batteries owing to its high specific capacity (>300 mA h g(-1)). However, the structural instability causes serious cycling degradation through irreversible insertion/extraction of NH4+. Herein, a new potassium ammonium vanadate K-x(NH4)(1-x)V4O10 (named KNVO) is successfully synthesized by a one-step hydrothermal method. The inserted of K+ can act as structural pillars, connect the adjacent layers closer and partially reduce the de-insertion of NH4+. Due to the multi-functional of K+, the prepared KNVO presents a high specific discharge capacity of 432 mA h g(-1) at a current density of 0.4 A g(-1), long cycle stability (2000 cycles, 94.2%) as well as impressive rate performance (200 mA h g(-1) at 8 A g(-1)).